Poulin played two seasons for the Stars, taking rookie of the year honours in 2008 and winning a championship in 2009, before spending four campaigns with Boston University. She left as the Terriers' all-time scoring leader.
The Beauceville, Que., native is best known for scoring both goals in a 2-0 win in the 2010 Olympic final and both the tying goal and the overtime winner in the 2014 final against the United States.
"My first choice was always to come back home to Quebec and have the opportunity to play for the Montreal Stars," Poulin said in a statement. "The team has a great leadership core with so many skilled players, it would be an honour for me to join such an exceptional group."
"Poulin's arrival is a game-changer for our league and for the Montreal Stars," said CWHL commissioner Brenda Andress. "With two Olympic gold medals to her name, she is bringing incredible international experience and a demonstrated ability to perform under intense pressure."
The CWHL Draft is on Aug. 23.